Video data storage devices are known in which broadcast quality video signals are transferred to and from storage at their display rate, also known as video rate or real time rate.
Data storage environments have become known in computer related fields which are capable of conveying signals having a greater bandwidth than that required for a real time video signal. For example, a raise of disks may be built, allowing each video frame to be divided into a plurality of stripes. Each stripe is then written to its own respective disk. Furthermore, redundant parity information may also be included, possibly on its own respective disk. In these environments, the bandwidth may be increased by increasing the size of the array, therefore it becomes possible to provide data transfers capable of conveying two video clips, three video clips or possibly more in real time.
Conventional controllers for transferring data in redundant arrays operate on a first-first come basis, such that a first requesting process will be allocated all of the available bandwidth. Thus, in a system capable of conveying data at three times video rate, this could result in a single data transfer being effected at three times the display rate while other processes are prevented from effecting a transfer. It has therefore been found that conventional arrangements for data arrays, used in environments where financial data is stored for example, are not suitable for the storage of video data. In this respect, it should be understood that video data may take the form of broadcast data at normal definition, where each frame consists of an interlaced field, non interlaced RGB frames, high definition video and digitised cinematographic film etc.
According to a first aspect of the present invention there is provided video data storage apparatus, comprising storage means, transfer means and processing means, wherein said transfer means is arranged to transfer video clips between said storage means and a plurality of processes, said storage means comprises a plurality of storage devices, and said processing means is configured to allocate individual frames to said processes so as to allow each process to transfer frames at a rate at least equal to video display rate.
In a preferred embodiment, the transfer means is arranged to transfer each frame at a rate substantially higher than said display rate, with extended periods occurring between the transfer of each frame to facilitate the transfer of frames belonging to other clips.
Preferably, the processing means is configured to guarantee bandwidth up to a notional maximum value. The transfer means may facilitate the provision of transfer bandwidth in excess of the notional value, wherein said processing means is configured to allow transfers beyond said notional value while not guaranteeing said transfers beyond said notional value.
According to a second aspect of the present invention, there is provided a method of storing video data, in which video clips are transferred between storage means and a plurality of processes and said storage means comprise a plurality of storage devices, wherein individual frames are allocated to processes so as to allow each process to transfer frames at a rate at least equal to video display rate.